Embodiments of the present invention relate to an image capture unit and methods of manufacture.
An image capturing unit 20 comprises a lens module 24 which directs an image onto an image sensor 28, as shown in FIG. 1. The lens module 24 comprises a lens 30 mounted in a lens barrel 32. The image sensor 28 comprises a CCD or CMOS array 36 having an image receiving side 38 that converts an incident image, which may be light, infra-red or other radiation, into an electronic signal. Typically, the image sensor 28 is enclosed in a package 40, and is fabricated by chip on board (COB), tape carrier package (TCP), or chip on glass (COG) methods. A holder 42 joins and aligns the lens module 24 to the image sensor package 40. The image capture unit 20 is used in, for example, electronic devices such as mobile phones, personal digital assistants, remote sensors, signal transmitting cameras; medical devices; and such applications such as lens for car security system.
However, it is difficult to fabricate conventional image units 20 at ever smaller sizes while still providing structural integrity, reliability, and ease of manufacturing and assembly. For example, conventional lens barrels 32 and the holders 42 are often made of injection molded plastic to facilitate mass production. However, injection molded lens barrels 32 and holders 42 are often difficult to fabricate to the precise dimensions needed to hold and align very small lenses having diameters of less than 1.5 mm. In addition, injection molding processes often form undesirable artifacts on the surfaces of the lens barrel 32, such as bumps and rounds, which interfere with subsequent assembly of a lens 30 into the lens barrel 32 and can even cause the lens to deviate from its proper position. Also, such plastic components often cannot withstand the high temperatures needed for fabricating other structures of the image capture units, such as for example, the temperatures used in semiconductor fabrication process such as a reflow process in wafer level packaging.
It is also often difficult to align or correctly position a lens 30 in a lens barrel 32 during manufacturing. In one process, a scale is printed on the inside surface 44 of the lens barrel 32 and the lens 30 is positioned to a point on the scale. However, even with this method, it is often difficult to properly position the lens 30 at an exact position on the scale as it is difficult to read the scale from outside the lens barrel 32. Further, it is even more difficult to position multiple lenses 30 in a lens barrel 32, as the individual lenses can be misaligned relative to one another or to the image receiving surface 38 of the image sensor 28.
Conventional image capturing units 20 are also difficult to assemble with proper alignment of the lens modules 24 and image sensors 28. For example, during assembly of the lens module 24 to an image sensor 28, fine dust falling on the image receiving surface 36 of the image sensor 28 can contaminate the surface and give rise to marks on resultant image signals. In addition, assembly of each image capturing unit 20 by manually assembling each lens 30 in a lens barrel 32, and then attaching the lens barrel 32 to an image sensor 28, is also labor intensive and involves many fine alignment steps during which one or more of the components can become misaligned. Alignment and contamination problems can also arise during assembly of a completed lens module 24 to a package 40 containing an image sensor 28, and attachment with an adhesive. The lens 30 has to be mounted at a precise distance from the image receiving surface 38 of the image sensor 28 to provide a suitable focal length. However, such assembly processes often fail to provide the precise alignment or distance of each lens module 24 and image sensor 28.
Thus it is desirable to have image capture units with lens and lens modules which have small sizes and precise dimensions. It is also desirable to have a method of manufacturing the lens modules that facilitates alignment of a lens in a lens barrel. It is also desirable to have a method attaching and aligning a lens module to an image sensor which reduces contamination, provides good alignment and focal distances, and still maintains a reasonable cost of assembly and fabrication.